The invention relates to a device for producing a printing form, wherein a radiation source acts pointwise or point-by-point on a material, for producing printing ink-accepting image points in accordance with a printing image. The material is applied to a printing-form blank which, during the imaging process, lies flat on a base or is clamped on a cylinder. In order to cover the entire image area, it is necessary to position a single radiation source or several radiation sources simultaneously parallel to the surface of the material and to activate the radiation source or sources pointwise or point-by-point in accordance with a printing image. It has become known heretofore, for example, to accommodate in a housing several semiconductor lasers at like spaced intervals, together with optically focussing mechanisms. To protect the optical elements, the light passage openings in the housing can be provided with protective glass. For radiation-physical reasons it may be necessary to dispose the radiation sources and the focussing mechanisms, respectively, as close as possible to the material upon which the imaging is to be performed. Particularly when the device for producing the printing form is located within a printing machine and facing towards a printing form cylinder, a risk arises of soiling the optical elements used when guiding the radiation by ink, dampening solution, dust, abraded paper particles and the like. Such soiling causes faults in the imaging operation. It is possible to employ special cleaning agents in order to eliminate the aforementioned soiling. In order to prevent soiling, electrostatic devices or air flows can be used to keep the foreign particles away from the optical elements and from the surface of the material on which the imaging is to be performed. Furthermore, it has become known heretofore to pivot or to shift an imaging head, including the radiation sources and the optical elements, away from the region threatened by soiling.
It is accordingly an object of the invention to provide a device for producing a printing form which, with little effort, prevents soiling of a radiation source and optical elements assigned thereto.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for producing a printing form, including at least one radiation source directed towards a material whereon an image is to be formed, and a device for positioning the radiation source in a direction parallel to the surface of the material, comprising a slide movable parallel to the surface of the material between the at least one radiation source and the material whereon the image is to be formed, the slide being formed with at least one opening and, when an image is being formed on the material, being positionable for allowing free passage through the at least one opening to a beam from the at least one radiation source, and, when no image is being formed on the material, being positionable as a shield between the material and the at least one radiation source.
In accordance with another feature of the invention, the slide and the radiation source are structurally integrated.
In accordance with a further feature of the invention, the printing-form producing device includes a plurality of the radiation sources arranged in a common housing at equally spaced intervals along a line in a positioning direction, the housing having thereon longitudinal guides for the slide, and the slide being formed with a plurality of the openings corresponding to the plurality of the radiation sources, the slide, when an image is being formed on the material, being positionable for allowing free passage through the plurality of openings to beams from the plurality of the radiation sources, and, when no image is being formed on the material, being positionable as a shield between the material and the plurality of the radiation sources.
In accordance with an added feature of the invention, the printing-form producing device includes an entrainer element formed on the slide and cooperating with at least one stationary cam, the housing being positionable out of a parked position for running the entrainer element onto the cam and moving the slide in the longitudinal guide into a position wherein free beam passage is provided, and the housing being positionable back into the parked position for moving the slide so as to close the beam passage openings formed on the housing.
In accordance with an additional feature of the invention, the cam is of bipartite construction.
In accordance with yet another feature of the invention, the slide is disposed on a U-shaped housing cover having a base portion formed with beam passage openings, and having legs with respective ends which are resiliently latchable into grooves formed in the housing.
In accordance with a concomitant feature of the invention, the housing cover is affixed to the housing in a direction corresponding to the direction of a generatrix of an outer cylindrical surface of a printing plate cylinder.
Thus, the objective of the invention is achieved with a device having the foregoing features. The invention ensures that those parts of the device which are threatened by contamination are automatically covered by the slide if the radiation source or the radiation sources are shifted from an imaging position into a parked position. The covering and uncovering, respectively, of the parts threatened by contamination are effected solely by driving the radiation source and the housing containing the radiation source, respectively. In this regard, the term radiation source is intended to include both a device for producing radiation, such as a semiconductor laser, as well as any equipment for forming and deflecting the beam, such as optical fibers, lenses with mounts, mirrors, aperture stops, light valves or tubes and protective glasses, and the like.